1. Field of the invention
The present invention relates to inkjet printers and more particularly to a method and apparatus for controlling mist associated with printer printhead maintenance.
2. Description of the related art
Inkjet printers typically employ a reciprocable carriage supporting one or more print heads. Printhead maintenance requires periodic jetting, sometimes called spitting, of ink droplets to clear contamination from nozzles or to ensure proper ink chemistry at the nozzle openings. The droplets are frequently collected in a waste ink reservoir called a spittoon. This ink droplet firing, as a part of a maintenance algorithm, occurs to clear the printhead nozzles of contamination or to prevent ink chemistry changes at the nozzle openings due to crusting, viscosity changes, or separation of ink constituents. A common problem is the fragmentation of the ink droplet during jetting. These fragmentary droplets are often referred to as xe2x80x9cmist.xe2x80x9d The mist may result in misting on the printed page, discoloring of features inside the printer, and, possibly, discoloring of articles surrounding the printer. Mist problems are exacerbated in color printers because the color inks are typically dye-based inks whereas the black ink is typically a pigment-based ink. The dye-based color inks are less dense and more prone to mist formation, and the mist which is formed lingers longer.
The jetting of ink and other maintenance tasks such as printhead nozzle wiping and capping are performed at a maintenance station at one extreme of printhead carriage travel. Sometimes, the printhead carrier will drag ink fog or mist along with it as it departs from the maintenance station to perform a printing task, contaminating other parts of the printer with waste ink.
A traditional method of controlling ink misting during maintenance is to provide a surface near the nozzle openings for ink mist and residue to accumulate. A surface and containment area is required for spitting of waste ink to maintain an inkjet printer printhead. In the past, inkjet printers have used hard surfaces onto which ink is spit to reduce satellites, which form mist. This technique takes advantage of viscous properties in the ink. The ink hits the surface and leaks down to a containment area. The disadvantage of a hard surface is that the more ink that is spit, the more rebound the ink has and the mist is still a problem as it will contaminate the printer. This surface and containment area is critical in keeping the waste ink and related ink fog or mist from migrating to other areas of the printer.
The assignee of the present invention has employed a spittoon in the form of a funnel having a foam filter material therein through which the jetted ink passed into an open waste ink containment area, however, ink mist within the open area was difficult to capture and sometimes escaped when the printhead was moved away from the spittoon preparatory to a printing task. Other techniques utilizing ventilating fans, spit wheels or capping the spittoon when not in use have also been suggested, but contamination due to printer ink mist remains a problem.
A surface is required for the color ink spitting of a printhead to maintain the print nozzles. This surface should contain and direct the waste ink flow to a desirable accumulation area in the printer. The present invention provides a surface in the form of a porous open cell foam spit surface and adjacent felt pad. The open cell foam allows the waste ink and air to pass through while maintaining some surfaces for the transport and collection of waste ink. Adjacent the foam is the absorbent pad for receiving and retaining the ink. The ink and air pass through the foam very quickly and efficiently and onto the collection surface. The open cell design of the foam allows the ink and air to pass through it without deflecting the vast majority of the ink volume. The foam is a hydrophobic foam to prevent the foam from absorbing the ink. The foam is also an ether-based material which is compatible with the inks.
The invention comprises, in one form thereof, a technique where waste ink which is jetted from an inkjet printer printhead toward an adjacent waste ink accumulating surface is confined and controlled by ejecting ink from the printhead into a hydrophobic open cell foam while laterally confining the ejected ink within the foam, and collecting the ink which passes through the foam in a closely adjacent felt pad. The felt pad functions as the waste ink accumulating surface. A printing operation is performed a fixed time interval after ejection of ink from the printhead. The printhead may be moved to a different location and ink ejected from a second printhead into the hydrophobic open cell foam during the fixed time interval.
An advantage of the present invention is that the foam and pad combination is better able to collect the ink and maintain a way to transfer the waste ink to the containment area.
Another advantage is the passing of this ink and air through the foam occurs very quickly and efficiently as is important to the printer function and thruput.